The present invention relates to a submarine cable power feeding system and, more particularly, to a submarine cable power feeding system for feeding power to submarine repeaters connected to submarine cables arranged in a matrix on a plane.
Hitherto, this kind of submarine power cable system for submarine cable devices is used to supply (“feed”) power to one, or a plurality of, submarine repeaters from a land power supply through a feed line, where the feed line serves as a submarine cable. The repeaters are connected in series and located on the sea bottom. A method for feeding power to a plurality of submarine repeaters connected in series from a land direct current (DC) constant-current power supply through a feed line (sub-marine cable) is disclosed, for example, in an article entitled “KAITEI DOUJIKU KEIBURU TSUSHIN HOUSHIKI (submarine coaxial cable communication system)” by Seiichi Shimura, page 182, published on Mar. 25, 1979.
However, the above conventional systems have the following problems.
In the case of a constant-current power feed, it is impossible under land-based power feeding control to branch a feed line, serving as a submarine cable, to expand the arrangement of submarine repeaters into a matrix configuration on a plane. The reason is as follows. Loads on branch cables vary depending on the number of submarine repeaters connected after branching. The current consumption of a given branch is a function of each submarine repeater, and the length of the branch feed line, so that currents of the respective branches are different from each other. Thus, the power needed to be supplied to each repeater cannot be achieved with a conventional matrix configuration.
Constant-voltage parallel power feed and alternating-current (AC) power feed are not included in the existing technique for the submarine cable system. The constant-voltage parallel power feed and the AC power feed have the following problems.
For the constant-voltage power feed, a feed line as a submarine cable can be branched. However, it is necessary to extend the range of input voltages in a power supply unit of each submarine repeater. The reason is as follows. As a cable connecting the submarine repeaters becomes longer, terminal voltages of the respective submarine repeaters are not equivalent to each other due to a voltage drop caused by the resistance of the cable. It is necessary to fabricate a power supply unit of each submarine repeater in accordance with the specifications for the maximum input voltage.
Because in an AC power feed, voltage can be freely changed, land power feeding systems often use an AC power feed. However, a submarine cable has a single-wire structure. The power efficiency of single-wire AC power feed is low. Accordingly, long-distance AC power transmission has shortcomings. Furthermore, in long-distance AC power transmission/feed, the frequency has to be lowered in order to improve the transmission efficiency. For this purpose, each of the repeaters requires a transformer which transforms the AC voltage at a low frequency to that voltage corresponding to the circuit of each repeater, respectively. This results in an increase in the size of the submarine repeater. Thus the AC power feed is not suitable for use in devices disposed on the sea bottom.